1. Field of the Invention
The present invention relates to a safety seat belt device for use in motor vehicles, and more particularly to a safety seat belt device comprising a lap and diagonal seat belt.
2. Description of the Prior Art
There has been known a safety seat belt device having a lap and diagonal seat belt for use in motor vehicles. In the known safety seat belt device, the seat belt extends upwardly from a retractor and passes through a through anchor. The seat belt has a distal end fixed to a vehicle body floor by an anchor, and an intermediate region inserted through a tongue. When the tongue is inserted in a buckle on the vehicle body floor, the seat belt has a shoulder belt portion extending diagonally across the thorax of the occupant between the through anchor and the tongue, and a lap belt portion extending across the lower waist or hip of the occupant between the tongue and the anchor.
When the seat belt is subjected to an abrupt tensile force upon a collision of the motor vehicle, the seat belt is prevented from being pulled out by a lock mechanism combined with the retractor for thereby holding the occupant from being thrown forward.
Motor vehicles may collide with another motor vehicle or object forward or rearward in a longitudinal direction or in a lateral or transverse direction. The seat belt device may be arranged such that when a motor vehicle collides with another motor vehicle or object forward or rearward, both the shoulder belt portion and the lap belt portion constrain the occupant, and when a motor vehicle collides with another motor vehicle or object laterally, only the lap belt constrains the occupant, and the shoulder belt portion does not constrain the occupant, so that any unnecessary constraint will not be given to the occupant.
The conventional lap and diagonal seat belt device has shoulder and lap belt portions as portions of a single continuous seat belt. Therefore, both the shoulder belt portion and the lap belt portion are locked by the lock mechanism when a collision occurs irrespective of the direction of the collision. If the shoulder belt portion is locked when the motor vehicle collides laterally, then the shoulder belt portion simply serves to hold the occupant against movement. It may be considered effective to prevent the shoulder belt portion from constraining the occupant upon a lateral collision of the motor vehicle.